create unique index IX_account_unique_email on account_unique (email); alter table account_constrain add constraint unique_account_constrain_email unique(email); 1. 2. 同样往两张表中插入相同的数据都不能继续插入。 我们可以看到两个表,虽然功能都能达到,但采用的方法是不同的。 那么到底这两种方法有...
CREATE UNIQUE NONCLUSTERED INDEX [IX_TestUnique_SiteIdUrl] ON [TestUnique] (SiteId,Url) 1. 2. 3. 消息1908,级别16,状态1,第1 行 列'Id' 是索引'IX_TestUnique_SiteIdUrl' 的分区依据列。唯一索引的分区依据列必须是索引键的子集。 --方式2 ALTER TABLE [dbo].[TestUnique] ADD CONSTRAINT [IX...
在Postgres中,可以使用done ()或lcase()来完成: CREATE UNIQUE INDEX lower_username_index ON enduser_table ((lcase(name))); PostgreSQL也有CITEXT数据类型,但不幸的是,HSQL似乎不支持它。我目前的版本是HSQL2.2.8和PostgreSQL 9.0.5。或者,其他内存中的数据库可能更适合测试SQL和PostgreSQL?提前感谢! 浏览1...
constraint_type有四种:UNIQUE、PRIMARY KEY、CHECK、FOREIGN KEY 通过修改上边sql语句的table_name和constraint_type来进行相应的查询 警告 本文最后更新于 December 28, 2017,文中内容可能已过时,请谨慎使用。
table_constraint 可以是以下选项之一:[ CONSTRAINT constraint_name ] { UNIQUE ( column_name [, ... ] ) [ USING INDEX TABLESPACE tablespace ] | PRIMARY KEY ( column_name [, ... ] ) [ USING INDEX TABLESPACE tablespace ] | CHECK ( expression ) | FOREIGN KEY ( column_name [, ... ] ...
createtabletest_1(idnumeric,namecharactervarying(100));altertabletest_1addconstrainttest_1_uqunique(id,name);--要提供外键,必须先建立唯一约束createtabletest_2(idnumeric,a_idnumeric,a_namecharactervarying(100));altertabletest_2addconstrainttest_fkforeignkey(a_name,a_id)referencestest_1(name,id);...
CHECK constraint– add logic to check value based on a Boolean expression. UNIQUE constraint– ensure that values in a column or a group of columns are unique across the table. NOT NULL constraint– ensure values in a column are not NULL. ...
save_point_1; SAVEPOINT for_test=# INSERT INTO consumers(id, consumer_id) VALUES (3, 'Bob'); INSERT 0 1 for_test=# INSERT INTO consumers(id, consumer_id) VALUES (1, 'Harry'); ERROR: duplicate key value violates unique constraint "consumers_pk" DETAIL: Key (id)=(1) already exists...
ADD CONSTRAINT film_rental_rate_check CHECK (rental_rate > 0 AND rental_rate IS NOT NULL); 在Navicat 表设计器中,相同的约束如下: 结语 检查约束是一个确保 PostgreSQL 数据完整性的强大工具。通过定义数据必须遵守的规则,可以防止插入或修改无效数据,从而帮助维护数据库的准确性和一致性。将检查约束纳入数据...
For example, if there's a unique constraint on a field such as a social security number, a user may not insert a duplicate row, meaning they can't access it, but they can deduce that a record with that social security number exists. By default, RLS is disabled on tables in...